Basal nitric oxide production in mouse collecting lymphatics does not enhance contractile activity

Abstract

The mechanisms governing spontaneous contractions in lymphatic vessels are incompletely understood. Accruing evidence in vivo suggests that basal levels of nitric oxide (NO) enhance lymphatic contraction amplitude, despite its well‐defined actions to inhibit contractile activity at moderate doses. Testing this hypothesis, we developed a method to isolate and cannulate collecting lymphatic vessels from the popliteal fossae of wild‐type (WT, n=12) and eNOS−/− mice (n=10). Diastolic diameter, contraction amplitude, and frequency were measured as a function of known pressure (1–10 cmH2O) in the absence of flow, first without then with the NOS inhibitor, L‐NAME. Vessels exhibited robust spontaneous contractions (53% of resting diameter) modulated by pressure, similar to other mammalian species. Contrary to current thought, inhibition of eNOS with L‐NAME (100μM) significantly increased the ejection fraction of WT vessels at low filling pressures (by 28% at 1–3 cmH2O, P<0.05); likewise genetic deletion of eNOS significantly (P<0.05) increased the contraction amplitude (by 45%) and ejection fraction (by 33%). Thus, when pressure and flow are controlled, basal NO production solely depresses lymphatic contractile activity. These data highlight isolated mouse lymphatic vessels as a powerful new tool enabling genetic models to be applied to lymphatic physiology for the first time. (NIH R01HL089784)